Techniques such as tomosynthesis and computed tomography (CT) are used for generating three-dimensional data from multiple X-ray images. Both these techniques should use accurate imaging positions in reconstructing the data. Any inaccurate positions for imaging, or mismatch between intended imaging positions and actual imaging positions, can lower the quality of the three-dimensional data.
Inaccurate imaging positions are caused by less accurate positioning of the stages that move an X-ray source, a camera, and an inspection object.
Producing higher-resolution images needs higher positioning accuracy. In the technical field involving increasingly smaller electronic components, for example, the imaging operation may be performed at a resolution as high as several micrometers. In such imaging, any less accurate positioning can lower the image quality for the reasons described below.
Under the same positioning accuracy, the quality of an image is affected more as the image has a higher resolution. This is because a positioning error creates a larger deviation in an image with a higher resolution. Additionally, the field of view is narrower (or the imaging area is smaller) for an image with a higher resolution, increasing the number of images to be captured. To shorten the time taken for the inspection, the stages are to be moved at high speed. Moving the stages at high speed can lower the positioning accuracy further.
Although the stages may be improved to increase the positioning accuracy, such improvement will increase the cost. Another possible solution may be to reconstruct the data after correcting the imaging position to an accurate position.
Preliminary learning a deviation between a target position and an actual position and correcting the imaging position based on the learning result is not effective. This is because the same deviation may not occur, and the deviation can vary in every imaging operation (due to repeatability error).
Patent Literature 1 describes a technique for calculating a positional deviation using values read during imaging by a sensor that is installed on a stage. More specifically, Patent Literature 1 describes a computed tomography (CT) apparatus for inspecting (imaging) an inspection object placed on a table while rotating the table. The CT apparatus detects the tilting of the table with the sensor, and determines any positional deviation in an imaging operation. The apparatus described in Patent Literature 1 performs such software correction to prevent deterioration of the image quality caused by unsteady movements of the table.